Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/1/2005
Publication Date: 12/1/2005
Citation: Leskey, T.C., Bergh, C.J. 2005. Factors promoting infestation of newly planted, non-bearing apple orchards by dogwood borer, synanthedon scitula harris. Journal of Economic Entomology. V98: 2121-2132. Interpretive Summary: Dogwood borer, the wood-boring clearwing moth, continues to be a threat to apple orchards in eastern North America due to burr knots produced by trees on dwarfing rootstocks. Little was known about when and where infestations began in commercial apple orchards or where infestations persisted. Therefore, we tracked infestation by dogwood borer on two cultivars, 'Gale Gala' and 'Sun Fuji' on two common dwarfing rootstocks, M.26 and M.7, from the time the trees were planted and for three years thereafter. Trees either were provided with a spiral wrap tree guard to prevent gnawing by vertebrate pests or left with bare trunks. We found that trees with tree guards produced more burr knots and had greater levels of infestation by dogwood borer by the third year. In a separate experiment, we evaluated the ability of a cultural control tactic, soil mounded just above the graft union of trees for 1-2 years, to prevent dogwood borer infestation. After two years, we removed the mounds and detected no infestation. However, burr knots present on mounded trees produced large amounts of rooting tissue and appeared to be more vigorous. Dwarfing characteristics of these trees was likely being lost due to rooting of the scion. Consequently, rooting tissue became infested by dogwood borer. Mounding, as described here, does not appear to be a desirable method for cultural control of dogwood borer.
Technical Abstract: The initiation and level of infestation by dogwood borer, Synanthedon scitula (Harris), was tracked over three consecutive years in two young, non-bearing apple orchards in West Virginia and Virginia. To improve our understanding of the factors that promote damaging levels of infestation by dogwood borer, the orchards were planted with trees representing a number of rootstock- variety combinations and were grown using different cultural practices. Infestations were detected during the first season after planting and continued to increase annually. The amount of burr knot tissue had the greatest impact on dogwood borer populations, as increasing amounts of burr knot tissue resulted in higher infestation rates. The use of plastic spiral wrap tree guards appeared to increase the development of burr knot tissue, resulting in significantly greater infestation compared with trees without tree guards on both M.26 and M.7 rootstocks in the West Virginia orchard. Variety also had a significant effect, as 'Idared' trees on M.26 rootstock had significantly greater levels of infestation compared with 'Buckeye Gala' on M.26, with or without tree guards, in the Virginia orchard. Mounding soil around the rootstock to a height just above the graft union prevented or tremendously curtailed infestation by dogwood borer, but led to scion rooting and loss of the size-controlling features of dwarfing rootstocks. Removal of the mounds at the beginning of the third growing season resulted in infestation of the rooted tissue during the same season. Crabapple pollenizers planted in the orchard in West Virginia were also attacked by dogwood borer and appeared to be highly susceptible to infestation. As long as apple cultivars continue to be planted on size-controlling rootstocks, dogwood borer will likely remain a serious pest, requiring either chemical treatments or a behavioral control strategy, such as mating disruption, to protect trees from infestation and damage.